1. Field of the Invention
The present invention relates generally to wireless telephones that include noise canceling, and, more specifically, to a wireless telephone device in which secondary path modeling forms part of the noise canceling system.
2. Background of the Invention
Wireless telephones, such as mobile/cellular telephones, cordless telephones, and other consumer audio devices that provide two-way voice communications functionality, such as some tablet computers, are in widespread use. Performance of such devices with respect to intelligibility can be improved by providing adaptive noise canceling (ANC) using a microphone to measure ambient acoustic events and then using signal processing to insert an anti-noise signal into the output of the device to cancel the ambient acoustic events.
ANC operation can be improved by measuring the transducer output of a device at the transducer to determine the effectiveness of the noise canceling using an error microphone. The measured output of the transducer is ideally the source audio, e.g., downlink audio in a telephone and/or playback audio in either a dedicated audio player or a telephone, since the noise canceling signal(s) are ideally canceled by the ambient noise at the location of the transducer. To remove the source audio from the error microphone signal, the secondary path from the transducer through the error microphone can be estimated and used to filter the source audio to the correct phase and amplitude for subtraction from the error microphone signal. The output of the transducer contains reproduced downlink speech and/or other program material and in the case of a telephone conversation, a portion of the near-end speech so that a user hears their own voice in proper relation to the telephone conversation. The portion of the near-end speech that is injected in the transducer output signal is referred to as sidetone and contains ambient noise, as well. The output of the transducer also includes the anti-noise signal, which, unless the sidetone information is properly managed, can cause cancelation of the side-tone and/or instability or improper adaptation of the ANC system due to the presence of ambient noise in the sidetone signal. In particular, the secondary path estimate described above can be frustrated by the additional path from the ambient acoustic environment, through the near-end speech microphone and out through the transducer, due to the requirement to inject sidetone during a telephone conversation.
Therefore, it would be desirable to provide techniques for managing sidetone in an ANC system having secondary path modeling.